At present, a little over about 40% of waste plastics, which are discharged in an amount of about 5,000,000 tons annually in our country, are difficult to thermally crack to yield oil substances. Particularly, fire-retardant resin materials that contain fire-retardants, such as phosphates, bromides, etc., are widely used for bodies of personal computers and the like. Since the fire retardants impede hydrogen transfer reactions, or halogens are eventually mixed with the produced oil substances, the fire-retardant resin materials are difficult to convert to oil substances, in comparison with base matrix resins that are free from fire retardants. Decomposing these fire-retardant resin materials to yield oil substances entirely by a method that is less harmful to the environment and the human body leads to a reduction in waste materials and the attainment of fuel recycling or chemical recycling of waste materials. Accordingly, development of this method has been strongly required in recent years, now that the importance of environmental problems is highly stressed.